JPA。双向关联：ManyToOne。删除父项时如何删除关联？

Question

我有两个实体：Product 和 Category

  public class Category {
    @Id
    @GeneratedValue(generator = "inc")
    @GenericGenerator(name = "inc", strategy = "increment")
    private int id;

    @OneToMany(cascade =  CascadeType.PERSIST, mappedBy = "category")
    private Set<Product> products;
}

public class Product {
    @Id
    @GeneratedValue(generator = "inc")
    @GenericGenerator(name = "inc", strategy = "increment")
    private int id;

    @ManyToOne
    @JoinColumn(name = "categories_id")
    private Category category;
}

我想在删除父项（类别）后将我的子项（产品）保留在数据库中（category 的值等于 null）。目前，当我尝试删除类别时，出现此错误：

org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException: Referential integrity constraint violation: "CONSTRAINT_F2: PUBLIC.PRODUCTS FOREIGN KEY(CATEGORIES_ID) REFERENCES PUBLIC.CATEGORIES(ID)

Answer 1

在删除类别之前，您需要更新关联。例如：

Category category = ...
for (Product p : category.getProducts()) {
   p.setCategory(null);
}
category.getProducts().clear();
entityManager.remove(category);

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